As the next generation of flat displays, there have been growing expectations for organic EL displays that use organic electroluminescent (EL) elements. The organic EL display has the advantages of being self-light emitting and independent of view angle, as well as being capable of achieving high contrast, slimness, lightweight, and low power consumption.
Organic EL elements, a component of an organic EL display, are generally disposed on a glass substrate in a matrix pattern. Each of the organic EL elements includes a first electrode (anode), a second electrode (cathode), and an organic layer disposed between the first and second electrodes. The organic layer includes a light-emitting layer containing fluorescent molecules, a thin hole-transportable layer, and a thin electron-transportable layer, wherein the light-emitting layer is sandwiched between the hole-transportable layer and electron-transportable layer. Application of voltage between the anode and cathode of an organic EL element causes holes injected into the hole-transportable layer from the anode and electrons injected into the electron-transportable layer from the cathode to be recombined in the light-emitting layer, causing the light-emitting layer to emit light. The organic EL elements are generally protected against ambient atmosphere by a protective layer.
The organic layer's thickness and thickness uniformity thereof are important factors during manufacture of an organic EL display, as these factors greatly influence light emission efficiency and power consumption of organic EL displays.
Examples of forming methods of organic layers include, for example, inkjet printing wherein coating solutions of organic materials are applied (printed) onto necessary areas followed by drying the solutions, and vacuum deposition wherein a metallic mask is used to deposit organic layers at necessary areas exclusively. With these methods, foreign substances could be introduced into organic layers.
In the inkjet printing method, it is possible that during application of coating solutions of organic materials foreign substances attached to the inkjet nozzles fall and are introduced into the resultant organic layers, or that foreign substances located inside the inkjet printing machine are discharged and scattered to be introduced into the organic layers. On the other hand, with the vacuum deposition method, it is possible that foreign substances in the deposition source are splashed and introduced into organic layers, or that foreign substances scattered from the vacuum chamber's inner walls or metallic mask are introduced into the organic layers.
In particular, recent requirements for large-size displays have also led to the development of large-size organic EL displays. Whether inkjet printing or vacuum deposition is used for the formation of organic layers, the chances that foreign substances are undesirably introduced into the organic layers are high, triggering quality reductions in organic EL displays.
Unwanted introduction of foreign substances into the organic layer results in current leakage between the anode and cathode, thereby increasing power consumption. Moreover, since less current flows near the foreign substance in the organic layer, brightness unevenness occurs, and occasionally, light emission failure occurs in a region near the foreign substance.
Unwanted introduction of foreign substances into organic layers during manufacture of an organic EL display causes problems like short circuits in the organic EL elements. In order to avoid these problems methods have been proposed in which a defective organic EL element is repaired by insulating foreign substances introduced in the organic layer after manufacture of an organic EL display (see, e.g., Patent Literatures 1-8).
Patent Literature 1 discloses, as illustrated in FIG. 1, a method of destroying anode 2 at a region under foreign substance 6 by irradiation with femtosecond laser beam 12 using laser oscillator 13 so that multiphoton absorption exclusively occurs at the irradiated portion of anode 2. This reduces possible damages to regions other than the defective part, and prevents current leakage between the anode and cathode through the defective part.
Patent Literature 5 discloses, as illustrated in FIG. 2, a method of preventing current leakage by selectively destroying second electrode 4 by laser radiation in such a way that the destroyed portion surrounds foreign substance 6 so that the region in which foreign substance 6 is introduced is insulated. Specifically, the method disclosed by Patent Literature 5 involves destroying second electrode 4 at a region around foreign substance 6, to form electrode-destroyed part 14 that surrounds foreign substance 6.
Patent Literature 7 discloses a method of preventing current leakage by applying, after manufacture of a display, a laser beam of relatively low energy to the organic layer at a region around a foreign substance. Radiating a laser beam of relatively low energy to a region of the organic layer around the foreign substance eliminates the layer structure in that region, whereby the irradiated region of the organic layer becomes highly electrically resistive.
Other prevention methods of current leakage are also known in which a portion of the second electrode is destroyed by laser radiation in such a way as to surround a foreign substance so that the region in which the foreign substance is introduced is insulated (see, e.g., Patent Literatures 9 and 10).
However, the methods as disclosed by Patent Literatures 1-10, which involve laser radiation after the formation of the second electrode, cause damages to layers other than those in which foreign substances are introduced, e.g., an electron injection layer or electrodes, which may conversely cause more defects in the organic EL display by laser irradiation.
In order to overcome these drawbacks, methods have been proposed in which foreign substances are rendered harmless immediately after the formation of organic functional layers in which the foreign substances have been introduced (see, e.g., Patent Literatures 11 and 12).
Patent Literature 11 discloses a prevention method of current leakage by forming insulating layers that cover foreign substances introduced. Patent Literature 12 discloses a method of repairing organic EL elements by removing foreign substances, introduced in the organic layers, by laser radiation and applying coating solutions of organic materials into the space from which the foreign substances have been removed.